atom is a "hackable text editor for the 21st century" created by the team at github. it's designed to be customizable, but also usable without needing to edit a config file.

this quote really sums it up perfectly:

because we spend most of our day in a text editor, the single most important feature we wanted in an editor was extensibility. atom is built with the same open source technologies used by modern web browsers. at the core of atom is chromium, the open source project behind google chrome. with that comes all the power and innovation being developed for the web. but more importantly, extending atom is as simple as writing javascript and css, two languages used by millions of developers each day.